import  pandas as pd
df=pd.DataFrame({'商品':['苹果','香蕉','梨'],'单价(元)':[5,5,4],'销量（kg)':[100,None,None],'库存(kg)':[50,None,None,70]})
print('原始数据:  \n', df)
print('检查缺失值: \n',df.isnull())
print('检查非缺失值: \n',df.notnull())
print('统计每列缺失值的个数: \n',df.isnull().sum())